Organizations which receive a lot of mail have automated and semi-automated labor-saving devices to handle and open the mail, by orienting and slitting the envelopes and extracting the contents for processing. There are various types of commercial machines that are well suited to handling envelopes that are of nearly the same size, such as for instance standard envelopes bearing payments for a utility company. In essence, such machines must first singulate envelopes, that is, select and feed one envelope after another from a stack, so they can be slit or otherwise processed one by one.
However, when the envelopes within a lot being processed vary in shape and especially thickness from piece to piece, then many prior art machines are less effective at singulating. Thick envelopes will jam at the singulator nip if the machine is configured for thin envelopes. Mis-feeding, of multiples of thinner envelopes, occurs when the machine is configured for the thicker envelopes. Thicker envelopes tend to have somewhat variable and indefinite wedge shape edges. Larger and thicker flat envelopes present special problems because they resist aligning against a downstream hopper surface in orderly fashion, and may even be shingled in the direction opposite of the direction of feeding. Whether or not thickness varies greatly, intermixed large and small shape envelopes present handling problems.
Another problem that attends many commercial envelope handling machines is the tendency for roller or belt surfaces to become fouled by debris picked up from the surfaces of the envelopes or other articles. When that occurs, frictional engagement with the articles diminishes, and any singulating or feeding action becomes impaired. To restore functionality, the machine has to be stopped so the rollers or belts can be cleaned or replaced.
The weight of a stack can create high inter-envelope friction among the bottommost envelopes, impeding singulating. On the other hand, when there are hardly any envelopes in the hopper, poor feeding and singulating can take place because of low friction in the system. Thus, there tends to be a need for continuing operator intervention, to correct deviations, or to maintain the hopper stack within some maximum and minimum range. Still another problem with prior art machines is that when envelopes, particularly ones which vary in size and shape, are put in a hopper for feeding to a singulator or document handling device, there is a tendency for them to “hang up”, or to lightly wedge in the hopper, and to cease dropping down as each bottommost envelope is fed away. A machine will then cease processing of items until the operator intervenes to aid the downward feeding manually.
Thus, even though there has been a lot of past development, and there have been many designs of machines for handling envelopes and other flat objects, there continues to be a need for improvements in the ways that have been mentioned.